Can't log in to site after upgrade

Tried to upgrade to latest version of WordPress but couldn’t because my php version is not updated. Downloaded new version of php but still could not upgrade WordPress. Then I updated my plugins and now I cannot log in to the site and have a screen full of error messages.

I seriously doubt that Akismet is the problem. Try re-activating it and deactivating all of your other plugins. If this works, re-activate the plugins one by one until you find the real problematic plugin(s).

Well, Akismet definitely is the problem. Even when I deactivate all other plugins, as soon as I download a new version of Akismet I can no longer access my site. De-activate Akismet and everything is fine. I know that millions of WordPress bloggers use Akismet but the latest version simply won’t work with my site.